It is often desired to keep an observation member directed towards an object in motion, for instance a telescope towards an airplane. Even if the object in question is moving with a constant speed, the control signal necessary for keeping the member directed towards the object is very complicated. This is especially true when the object is close to the observation member. This causes great difficulties in tracking even when the control member is controlled manually by an operator.
It is known that manual control can be aided in tracking an object moving at a non-uniform speed by a control signal for constant speed tracking since the constant speed terms are still dominant.
A plurality of devices for generating such control assistance to manual tracking have been described before. All of them use, in one way or another, the equations indicating that the measuring point defined by the target observing member is moving at a substantially constant vector speed.
An example of a known solution utilizes the fact that the right-angled components of a constant vector speed in a non-rotating coordinate system also are constant is evident from, for instance, Swedish patent 158,659.
Another known solution utilizes the fact that if the component of the vector acceleration perpendicular to the radius from the observation point to the target is zero, then the law of Kepler says that the product of the distance squared and the angular velocity is constant. An example of this solution is shown in Swedish patent 336,748.
In all of the above cases, target tracking members are employed which must measure the distance from the member to the moving object.
A great many applications exist where control aid is wanted, in a situation where it is not practical to measure the distance at all or, at any rate, not continuously. This same problem exists in fire control systems so that the solution set forth herein is applicable thereto.